> How do I go about teaching pkgsrc about the Solaris OpenSSL?

If you don't want to teach pkgsrc (as mentioned in the other response from 
Juan), then you can just tell pkgsrc to use your native OpenSSL.

Try:

USE_BUILTIN.openssl=	yes
PREFER_NATIVE+=	openssl
PREFER.openssl=	native

(I think you could use any of the above in your mk.conf.)

Be sure to do a "bmake clean" first to remove any cached settings.

  Jeremy C. Reed